The invention relates to a method for performing an X-ray diffractometry analysis of a crystalline and/or amorphous sample, by means of an optical X-ray apparatus with an X-ray source that has an X-ray anode constructed from a mixed configuration of at least two metals.
Such an X-ray anode is known from DE 195 36 917 A1
In X-ray diffractometry (XRD), discrete X-ray energy (usually K-alpha radiation of the anode material) is used to generate interferences (reflexes) on three-dimensional periodic structures at an atomic scale (crystals) according to Bragg's Law. The angle and intensity of the reflexes contain important information about the atomic and micro structure of the substances to be analyzed.
Therein, certain material characteristics of the crystal samples can be analyzed and determined by special X-ray line energies. These include not only absorption, anomalous dispersion, measurable angular range, disturbing or useful X-ray fluorescence signals of the sample, but also additional wavelength-dependent effects. Metals typically used in XRD X-rays are Cu (1.54184 angstrom), Co (1.7906 angstrom), Cr (2.29100 angstrom), Fe (1.93736 angstrom) and Mo (0.71073 angstrom) and for example, Ag (rel. high energies) is also sometimes used.
Typical applications/analyses for the various characteristic energies: Cu radiation is suitable for most XRD analyses, while Mo radiation is preferred, for example, for the analysis of steels and metallic alloys in the range Ti (A=22) to around Zn (A=30). Co radiation is often used in conjunction with samples containing Fe as it is often not possible to avoid disturbing iron fluorescence radiation in any other way. Fe radiation is also used, for example, for samples containing Fe and for minerals where Co or Cr radiation cannot be used. Cr radiation is suitable for complex organic substances and stress measurement of steel. Characteristic W radiation can only be excited when electron energies are very high. W tubes are therefore used if radiation continuity is more important than individual lines and they are not suitable for XRD measurements.
Until now, the aim has always been to use X-ray anodes for XRD which are made of pure element metals because, without the ability to discriminate between energies, metal impurities in the anode material can result in disturbing reflexes in the diffraction image and misinterpretation of the measurement result. For cost reasons, a scintillation counter is often used which, although extremely sensitive and able to detect individual photons, it is not able to resolve photon energies that are close together in the spectrum.
The X-ray tube on existing X-ray diffractometers is sometimes replaced in order to exchange the anode material and to prepare the diffractometer for measuring other samples. This conversion can be very time-consuming, since, as in most cases, the entire equipment has to be readjusted to the primary beam (including the detector electronics) that is directed onto the sample.
Many experiments have been carried out in the past with anodes made of alloys or other metal compounds.
In 1963, British patent GB1 032 118 A disclosed a method for manufacturing metal alloys with molybdenum or tungsten.
U.S. Pat. No. 3,778,654 A describes an X-ray anode made of a W—Mo alloy (for mammography). Mo is particularly suitable for the analysis of the affected boneless tissue. The strain placed on the anode by electron bombardment is considerable. The alloy of Mo with W in a particular proportion offers considerable advantages over anodes with pure Mo (robustness, lower therm. fatigue etc.).
U.S. Pat. No. 3,836,808 A, describes a rotating anode which is made of 75% Mo and up to 25% of a metal with an atomic number between 39 and 46 (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd). The patent describes how the effectiveness of anodes made of pure molybdenum decreases due to roughening. The alloys described are designed to minimize or delay roughening.
As long ago as 1943, anodes for X-ray apparatus for industrial/medical applications were described in British patent GB 551,897 A. The anodes described consist of a combination of a finely distributed phase of tungsten and a continuous phase of Cu, Ag, or Au. Such anodes exhibit a high X-ray output combined with a high resistance to electron bombardment and good thermal conductivity. They can also be manufactured by compression and sintering processes.
EP 0 062 380 describes a coated X-ray anode, consisting of W, Mo and a W—Mo alloy, as well as a method for manufacturing same. The patent describes the conditions (temp. etc.) under which certain layers can be applied by vacuum coating from the gas phase. The substrate is described as a combination of Mo, Ti, Zr and C. One of the layers is described as a combination of W and a W alloy containing portions of Rh, Ta, Os, Ir, Pt and similar elements. One layer is described that contains Re.
The primary objective of the development was to create durable, robust anodes and/or alloys, wherein only one specific energy line was used for the X-ray diffractometry itself.
U.S. Pat. No. 7,317,783 B2 discloses an X-ray anode that is composed of different metals in several zones. The electron beam can be aimed in such a way that only one zone is bombarded. In this way, the sample can be analyzed using individual energy lines of different pure metals. This invention is also intended to excite individual energy lines while eliminating the time-consuming conversion required to exchange the anode material.
DE 195 36 917 A1 discloses an X-ray anode for X-ray fluorescence (XRF) analysis. To ensure optimum excitation of XRF samples, several X-ray lines in the spectrum are desirable. An X-ray anode comprising a combination of several metals is the subject of the invention described in the publication. It enables multi-element analyses for XRF analyses. It is pointed out that basically all stable metal mixtures/alloys can be used, although Mo and W, in particular, are advantageous. Such an anode is advantageous for X-ray fluorescence analysis but unsuitable for X-ray diffractometers with scintillation counters.
In recent years, the use of energy-dispersive semi-conductor detectors has increased at an ever increasing rate; the gradual reduction in price being one of the reasons for this. These detectors can very precisely assign the measured photons to an energy in the X-ray spectrum. Even low-cost detectors achieve resolutions in the range of a few hundred electron volts. This makes it possible to separate and individually evaluate typical characteristic energy lines (see list above) in the spectrum. Even K-alpha and K-beta X-ray lines of an element (in the anode) can be separated from each other. Information is then obtained about the sample by means of a measurement (angle scan), which is derived from two different energies. Simultaneous measurement with 2 wavelengths (K-alpha & K-beta of the anode material) is already possible with the use of a suitable detector (XFlash from Bruker nano).
The object of this invention is therefore to present a method by which X-ray diffractometry analyses with multiple characteristic energy lines are possible without any need for conversion or switchover.